Do Narcissists Know They're Narcissists?

According to a provocative paper just published, it’s possible to accurately determine how narcissistic someone is by asking them just one thing.

Here’s the question in full:
To what extent do you agree with this statement: I am a narcissist? (Note: The word ‘narcissist’ means egotistical, self-focused, and vain.) Answer on a scale from 1 (not very true of me) to 7 (very true of me).
According to psychologists Sara Konrath and colleagues, complex personality tests and lengthy questi